This invention relates to rotating filter disks; more particularly, this invention relates to a modular filter disk in which individual sectors--to create a disk--are removably mounted on towers which support, and may also drain, the sectors as they are rotated into, and out of, a slurry.
The prior art is replete with disk filters utilized to filter slurries such as might exist, for example, in the paper and pulp industries. Typically, and especially in larger sizes, the disks are comprised of adjacent sectors mounted on a rotating shaft so that successive sectors of the disk are rotated into, and subsequently out of, the slurry. During the immersion of each sector in the slurry, a pressure differential is applied to the sector causing the liquid in the slurry to flow through flow channels in each sector toward a central core, or drainage, channel while a so-called filter cake adheres to, and builds up on, the outside surface of each sector.
Upon emergence of a sector from the slurry, a filter cake has built up on each sector and this cake is removed, first by ceasing application of the differential pressure and then, subsequently, by the application of a knock-off shower designed to peel away the substantially dry cake which has adhered to the sector. This cake is then collected prior to the re-entry of a sector into the slurry to begin another cycle.
Demands for increased filtration capacities have led to ever increasing filter sizes, with some commercial applications now ranging to 18" or more in diameter. When, as is inevitable, maintenance requires the repair or replacement of sectors, the sector structure has to be dismantled from the hub on which the sector is mounted. Not only is the removal process awkward because a worker has to get into the crowded space around a hub to dismantle a sector, but sector size and weight dictate possibly two or more workers to manage the removal operation.
As those skilled in the art will appreciate, once the filter cake has built-up on a sector and the pressure differential has been removed prior to the filter cake removal from the surface of a sector, re-wetting of the essentially dry filter cake by filtrate--insufficiently drained from the sector structure--dribbling in reverse flow, so to speak, may occur.
Accordingly, it would be advantageous to create a modular assembly so that certain parts of what would be a normal sector installation remain more or less permanently affixed to the rotating hub while the individual sectors can be simply and separately unbolted in a one man operation. It would also be advantageous to provide a disc sector having improved anti re-wet features.